When downhole activities are required in wells being drilled and completed it is frequently necessary at times during drilling operations to conduct well bore logging activities during which a logging tool is run into the well in order to evaluate the progress of the well bore and to identify various characteristics of the earth formation being traversed by the well bore. These operations are typically carried out by running logging tools into the well by means of wireline cables. Various other well servicing activities are carried by means of tools that are run into well bores or well casing by means of wireline apparatus. Especially when wells are being drilled and completed high pressure conditions are often encountered such as when production formations are intersected by the well bore.
When wireline operations are being conducted especially under conditions of high well pressure, wireline risers of significant height are often employed in order to provide the wireline apparatus with sufficient pressure containing capability to insure against the possibility of a well blowout through the wireline apparatus. These wireline risers incorporate grease wipers and wireline packers in addition to a wireline blowout preventer to thus render the wireline apparatus safe from the standpoint of containing well pressure. Typically an open sheave is mounted above the wireline riser and the wireline being run into or exiting the well extends about this upper sheave and thence downwardly to a lower sheave near ground level in route to a wireline winch which is typically mounted on a wireline service vehicle.
Of late, rather than providing extremely tall wireline risers especially under conditions where the height of the wireline riser is restricted, it is deemed desirable to provide a pressure containing sheave which is located at the upper end of a wireline riser of limited height and to provide a grease seal conduit extending downwardly from the pressure containing sheave head to thus achieve wireline containing apparatus of sufficient length for efficient pressure containing capability. An example of a pressure containing sheave disposed in pressure connection with a wireline riser and a grease seal conduit is presented by U.S. Pat. No. 5,188,173 of Richardson, et al. This type of pressure containing sheave has deficiencies in that it is restricted from the standpoint of pressure containing capability. The housing is subject to considerable pressure induced side loading, which, especially under high pressure conditions can significantly distort the body structure to the extent that the sheave can become inoperative. It is desirable therefore to provide a pressure containing sheave mechanism for wireline well servicing apparatus and for other activities.
As the wireline emerges from a well such as when a well tool is being raised to the surface the wireline is typically coated with well fluid within which is entrained contaminates from the well. Even though the wireline is passed through grease filled risers and grease wipers a certain amount of the well contaminates will be present on the wireline as it passes over the upper wireline sheave. While this is not a particular problem from the standpoint of open wireline sheaves when wireline sheaves are closed and adapted for containing well pressure the contaminates on the wireline can migrate to the sheave bearings so that the bearings can become fouled with the well contaminates. Under this condition the bearings will rather quickly deteriorate to the point that the sheave mechanism will need to be repaired or the sheave will require replacement. It is desirable therefore to provide a pressure containing sheave mechanism which effectively prevents migration of well contaminates from the wireline groove of the sheave to the sheave bearings. Virtually all wireline sheaves incorporate a sheave body structure having a sheave wheel rotatably located therein and having a large circular closure plate which is typically bolted to the sheave body and serves as a sealed retainer for the sheave wheel. The large circular seal for sealing the closure plate to the sheave body defines a very large closure plate area that is subject to pressure induced side loading. To withstand high pressure the closure plate must be of considerable thickness to withstand the influence of pressure on its substantially large pressure responsive area and a large number of large bolts of considerable length are typically required to secure the closure plate against the high pressure induced side load. It is desirable therefore to provide a sheave wheel assembly employing seals which minimize the pressure responsive area of the sheave chamber closure and thus minimize the side loading to which the sheave housing is subjected throughout the entire pressure range of the sheave mechanism.